Why is this parallel path only a problem on the load side of the service disconnect??? There are often multiple parallel paths on the line side. What makes it safe on the line side, and under the same conditions, unsafe on the load side?
As far as using an EGC for the subpanel, in one respect it is not better. The grounded conductor will be larger than the EGC and make a better fault clearing path than using the fourth wire for a remote building subpanel.
Don
